Installation Guide RN5000US
14
the output of the Digiwatts perfectly.
The Digiwatts system incorporates an advanced
active islanding protection algorithm to ensure that the system will not export power into
a balanced 60 Hz resonant load while the utility is disconnected.
The Digiwatts system
periodically injects both leading and lagging reactive current into the utility grid.
This
method has been proven by independent test labs to effectively destabilize and
disconnect from a balanced island condition.
PV Insulation Fault Detection
Before the inverter connects to the grid, the Digiwatts system will detect the isolation of
PV+ and PV- to the ground.
When the insulate impedance is less than 1M
Ω
, the
inverter will not function.
After the inverter is connected to the grid, the system will
detect the residual current.
If a residual current greater than 30mA is detected, the
Digiwatts system will shut down and display a fault condition on the LDC user interface
display.
AC Overcurrent Protection
The system will detect the AC current real time.
Should the AC current exceed 50
ampere, the Digiwatts system will shut down and display a fault condition on the LCD
user interface display.
Surge Protection
Over-voltage protection though the use of surge protection devices (SPDs) or surge
arresters should be provided when the PV power system is installed.
The Digiwatts unit
is not equipped with SPDs on either the PV input side or AC output side. Lightning can
cause damage either from a direct strike or from surges due to a nearby strike. Induced
surges are the more likely cause of lightning damage in the majority of installations,
especially in rural areas where electricity supplies are usually by long overhead lines.
Surges may be induced on both the PV array conductors and the AC cables leading to
the building. The risk of a direct lightning strike into a building can be mitigated by using
appropriate external lightning protection configured to discharge lightning current to
ground.
Specialists in lightning protection should be consulted regarding the
